The present invention is a method for making industrially important aromatic-substituted (hydrocarbonoxy)silane compounds which are utilized in, for example, silane coupling agents. Hydrido (hydrocarbonoxy)silane compounds, as typified by SiH-functional alkoxysilanes, are important intermediates for modified silicones, in the surface modification of various types of substrates, and as crosslinking agents in curing reactions of polymers.
Aromatic substituent groups are introduced onto hydrido (hydrocarbonoxy)silane compounds for various purposes, including improvement of heat resistance, control of refractive index, and improvement of compatibility with other organic compounds or polymers. Such compounds containing aromatic groups include phenylsilicon compounds in which aromatic rings are bonded directly to silicon atoms, as typified by phenylsilane compounds and phenylsilicon derivatives; and aralkylsilicon compounds in which aromatic rings are bonded to silicon atoms via hydrocarbon groups such as benzylsilane compounds or silicone derivatives which have 3-phenylpropyl groups or phenethyl groups. Among these compounds, phenyl groups bonded directly to silicon atoms can be manufactured by the reaction of metallic silicon with chlorobenzene (i.e., ie so-called direct method), a dehydration reaction between benzene and hydridochlorosilane by means of a boron chloride catalyst, or an equivalent organic reaction such as the Grignard method. Aralkylsilicon bonds can also be made by an equivalent organic reaction such as the Grignard method, however the making of 3-phenylpropyl groups or phenethyl groups can be accomplished more economically using a hydrosilylation reaction of aromatic compounds which have unsaturated groups, such as allylbenzene or styrene. In particular, numerous vinyl-substituted forms of aromatic compounds such as benzene, naphthalene, and pyridine and vinyl-substituted forms of derivatives of benzene, naphthalene and pyridine are known. Such compounds are commercially available and are optimal for the synthesis of silicon compounds which have various types of substituent groups. Generally, however, vinyl groups which are directly bonded to aromatic rings have readily polymerize, so that considerable portions are lost by polymerization when a hydrosilylation reaction is conducted over a long period of time or at a high temperature. In addition, a hydrosilylation reaction of vinyl groups bonded directly to aromatic rings is poor in terms of positional selectivity of the addition, so that the product is a mixture of 2-arylethylsilicon compounds and 1-arylethylsilicon compounds and the separation of these components is difficult. Furthermore in hydrosilylation reactions it is frequently necessary to add oxygen to the reaction atmosphere in order to realize and maintain catalyst activity, therefore there is a danger of ignition and explosion.
The object of the present invention is to solve the two problems involved in the abovementioned hydrosilylation reactions of vinyl-substituted aromatic compounds, that is (1) the low positional selectivity of addition and (2) the fact that high-temperature or long-term hydrosilylation reactions must be avoided in order to avoid polymerization of the vinyl groups.
The present invention is characterized by the following: in a hydrosilylation reaction using a platinum or platinum compound catalyst the positional selectivity of addition is greatly improved and the reactivity is improved at a low oxygen partial pressure or in the absence of oxygen by causing a carboxylic acid compound to be present in the reaction system when a hydrido (hydrocarbonoxy)silane compound with a low reactivity is reacted with an aromatic vinyl compound.